1. Field of the Invention
The present invention relates to a method and apparatus for cleaning a diesel particulate filter for a motor vehicle.
2. Description of the Prior Art
Diesel engines are efficient, durable and economical. Diesel exhaust, however, can harm both the environment and people. To reduce this harm governments, such as the United States and the European Union, have proposed stricter diesel exhaust emission regulations. These environmental regulations require diesel engines to nearly meet the same pollution emission standards as gasoline engines.
One part of diesel exhaust includes diesel particulate material. Diesel particulate material is mainly carbon particles or soot. One way to remove soot from diesel exhaust is with diesel traps. The most widely used diesel trap is a diesel particulate filter which nearly completely filters the soot without hindering exhaust flow. As a layer of soot collects on the surfaces of the inlet channels of the filter, the lower permeability of the soot layer causes a pressure drop in the filter and a gradual rise in the back pressure of the filter against the engine. This phenomenon causes the engine to work harder, thus decreasing engine operating efficiency. Eventually, the pressure drop in the filter and decreased engine efficiency becomes unacceptable, and the filter must either be replaced or the accumulated diesel soot must be cleaned out.
The filter is cleaned of accumulated diesel soot by burning-off or oxidation of the diesel soot to carbon dioxide which is known as regeneration. Regeneration of an existing filter is superior to filter replacement, because no interruption for service is necessary.
In addition to capturing carbon soot, the filter also traps ash particles, such as metal oxides, that are carried by the exhaust gas. These particles are not combustible and, therefore, are not removed during regeneration. The filter must therefore be cleaned or discarded when the ash particles in the filter build up to high levels.
Cleaning ash from a diesel particulate filter is not easily accomplished with typical maintenance shop equipment. The use of shop air to blow out the ash particles does not lend itself to containment of the ash particles. The use of a wet/dry vacuum tool has limited effectiveness on smaller and deeply embedded particles. The use of water or solvents can be detrimental to the substrate and/or washcoat.
One method exposes the filter to excessive handling which increases the potential for inadvertent damage to this expensive component. This method also suggests precautionary methods such as paint masks, safety goggles, and gloves prior to servicing a filter due to the potential for exposure to the hazardous ash particles.
To avoid this dangerous mess, specialized filter cleaning equipment has been developed. There are two primary types of cleaning machines. The first type is a pulsed air cleaner. The pulsed air cleaner blasts a pressurized charge of air through the filter from the back-side and accumulates the ash in a large filter within the machine. The pulsed air cleaner operates within a 20 minute cycle and is used for most dirty filters. However, in some conditions the truck aftertreatment system does not properly initiate a regeneration cycle to burn the soot burning cycle, and the filters become plugged with sticky soot. It is impossible to blow out the soot plugged filters with the conventional pulsed air cleaner.
The second type of cleaning machine is a thermal regenerator. The soot plugged filter is heated in a thermal regenerator for a period of time to convert the soot to ash. The filter is then removed from the thermal regenerator and subsequently treated with a pulsed air cleaning machine to clean the filter. The thermal regenerator requires from 3 to 7 hours.
This equipment, however, is expensive to purchase for the service shop, which would make the cost of cleaning expensive for the motor vehicle owner. The machines take up a large amount of space in a typical shop. Both types of machines require compressed air sources, 110V electrical sources, and the thermal regenerator requires a 30 A 240V circuit as well.
Therefore, it would be advantageous to develop a method to quickly and easily clean the diesel particulate material from the filter, such as the ash particles and possibly the soot, especially without first baking the filter in a thermal regenerator. It would be further advantageous to clean the filter without using costly equipment or to develop a method using parts that are readily available in a service shop. It would also be advantageous to develop an apparatus that is easy to use and economical.